I've had a variety of folding knives, but I keep coming back to the Spyderco Delica 4, or the Salt 1 if I need the corrosion resistance.
My first "real" folding knife was was a Mini-Griptilian with the oval thumbhole and combo-edge sheepsfoot blade.
I recently picked up a Kershaw Leek. The auto-opener is neat, but I leave the lock engaged because I'm worried about it opening in my pocket, so it's kind of awkward to use quickly.